It's not clear exactly why Dallas has had so many cases of West Nile, but there are several theories.

Like the rest of the country, Dallas experienced a mild winter, but it also had several rainstorms in the spring. Standing pools of water make the perfect breeding grounds for mosquitoes, Magori said.

Though no one has done a thorough survey of local birds, another theory is that Dallas-area flocks this year might have more young birds that have never encountered the virus. That allows more of them to become infected and then spread the disease to mosquitoes, said Erin Staples, a medical epidemiologist with the Centers for Disease Control and Prevention (CDC) in Fort Collins, Colo. Birds that were exposed in years past are immune to the disease, Staples told LiveScience. ::snipping2::

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" Everyone is entitled to his own opinion, but not his own facts." - Daniel Moynihan

The West Nile virus of 2012, which has caused one of the worst outbreaks in years with more than 100 cases inside Harris County alone as of Nov. 2, may be getting worse.

According to the Washington Post, two U.S. doctors are reporting troubling trends that affect the brain.

Dr. Art Leis in Mississippi is reporting the virus damaging speech, language and thinking centers of the brain, something he hasn't seen before - and much more encephalitis. Dr. Elizabeth Angus in Michigan tells the Post she's noticed brain damage in previously healthy patients, not just the sick and elderly.

Neurologists in Dallas also noticed more devastating encephalitis, the Post reported, but in different parts of the brain.

Marc Fischer, a CDC epidemiologist at the Centers for Disease Control and Prevention in Atlanta is not convinced of a mutation causing new types of brain damage, but that because of the sheer volume of cases means more serious cases are likely to occur.

In Galveston, University of Texas Medical Branch virologist Alan Barrett said viral samples from mosquitoes and birds in the Houston area show signs of genetic changes, the Post reported. ::snipping2::

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" Everyone is entitled to his own opinion, but not his own facts." - Daniel Moynihan

As of Tuesday, 48 states plus the District of Columbia had reported West Nile infections in people, birds or mosquitoes. Of the 5,054 cases involving people, 51 percent were classified as neuroinvasive disease (such as meningitis or encephalitis) and 49 percent were classified as non-neuroinvasive disease.

The 5,054 cases mark the highest number reported through the beginning of November since 2003. The bulk of reported cases are from 10 states -- California, Illinois, Louisiana, Michigan, Mississippi, Nebraska, Ohio, Oklahoma, South Dakota and Texas. The highest number of reported cases in any one state is in Texas (1,684 cases, 76 deaths), according to the U.S. Centers for Disease Control and Prevention.

The best way to avoid the mosquito-borne virus is to wear insect repellent and support local programs to eradicate mosquitoes. There is no treatment for West Nile virus and no vaccine to prevent it, according to the CDC.More...More information:http://www.cdc.gov/ncidod/dvbid/westnile/index.htm

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DALLAS (AP) — West Nile deaths were mounting quickly this summer as mosquitoes spread the virus across the country. The situation was especially dire in Texas, where some authorities resorted to aerial spraying for the first time in decades to curb what became one of the worst such outbreaks in U.S. history.Nationally, more than 240 people died from the mosquito-borne illness — about a third of them in Texas.

Now with the mosquito population decimated by the cooler weather, health experts have turned their attention to learning lessons from the latest round of deadly cases. Federal health authorities are collecting data and examining potential factors, while Dallas County — the epicenter of the outbreak — has begun year-round mosquito surveillance and testing.

What remains unclear is whether experts will be able to shed light on what caused the outbreak, why parts of Texas were so severely affected and if they can forecast the next major surge in the illness. ::snipping2::West Nile virus is believed to have first appeared in the U.S. in 1999 in the New York City area and then gradually spread across the country. Mosquitoes get the virus from feeding on infected birds and then spread it to people they bite. Most people infected show no symptoms, but the most severe form of the disease, called neuroinvasive, can cause a coma, convulsions, muscle weakness, paralysis and death.

The Texas Department of State Health Services reported more than 835 neuroinvasive cases this year and 86 deaths, led by Dallas County's 18 fatalities. The national death toll this year approached historic numbers from 2002, when 284 people died from the disease.

Petersen said the CDC is trying to determine what caused the latest outbreak by looking at factors such as heat, rainfall and the number of migrating birds that transmit the virus to mosquitoes. The agency is also researching the genetics of the virus to see if it may have mutated, but that doesn't seem to have happened.

Petersen added that while a warm spring with ample rainfall in North Texas was likely a factor, it's not known exactly what caused so many cases in the area.

"Probably, there was just the right combination of warmer weather and enough rainfall and probably a good dose of bad luck as well," Petersen said. "These outbreaks are subject to a fair amount of random variation."

The situation became so severe in North Texas that the state paid for aerial spraying in areas of Dallas County and nearby Denton County. Dallas County had not conducted such an operation since 1966 when encephalitis was blamed for more than a dozen deaths.More...

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" Everyone is entitled to his own opinion, but not his own facts." - Daniel Moynihan

As of December 11, 2012, 48 states have reported West Nile virus infections in people, birds, or mosquitoes. A total of 5,387 cases of West Nile virus disease in people, including 243 deaths, have been reported to CDC. Of these, 2,734 (51%) were classified as neuroinvasive disease (such as meningitis or encephalitis) and 2,653 (49%) were classified as non-neuroinvasive disease.

The 5,387 cases reported thus far in 2012 is the highest number of West Nile virus disease cases reported to CDC through the second week in December since 2003. Eighty percent of the cases have been reported from 13 states (Texas, California, Louisiana, Illinois, Mississippi, South Dakota, Michigan, Oklahoma, Nebraska, Colorado, Arizona, Ohio, and New York) and a third of all cases have been reported from Texas.

West Nile data and maps available at above link.

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" Everyone is entitled to his own opinion, but not his own facts." - Daniel Moynihan